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Question #45078

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The Question

Consider the polyfunctional amino acid whose structure is given below: $\ce{HOOC - CH2 - CH(NH2) - CH(F) - COOH}$ The experimentally determined $pK_a$ values for its three ionizable groups at 298 K are 1.6, 3.6, and 9.4. A buffer solution of this amino acid is prepared at a pH of 2.6. Assuming the given $pK_a$ values correspond to the independent ionization of the respective functional groups, determine the ratio of the concentration of the ionized form to the unionized form of the C5-carboxyl group, $\frac{[\ce{C5-COO^-}]}{[\ce{C5-COOH}]}$ , according to IUPAC nomenclature rules.

Options

A.
$0.1$
B.
$10$
C.
$1.0$
D.
$0.01$

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Numerical_Precision

Improve calculation stamina and avoid rounding errors in high-stakes competitive examinations.

Concepts Behind This Question

IUPAC Nomenclature Priority|Amino Acid Zwitterion pH Sensitivity|Degree of Dissociation (α) approximation

Why This Question Is Tricky

Common Mistakes

The question tests the intersection of IUPAC nomenclature, electronic effects, and ionic equilibrium.

The primary trap is the 'Hidden Variable' of IUPAC numbering direction.

Students habitually number from left to right, which would incorrectly identify the rightmost carbon as C5.

If they do this, they will assign the lower $pK_a$ (1.6) to C5 due to the adjacent fluorine atom, leading to a calculated ratio of 10 (Option B).

This penalizes rote application of the Henderson-Hasselbalch equation without rigorous structural analysis.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Organic Chemistry – Some Basic Principles and Techniques - Class 11 Part 2
Concept	IUPAC Nomenclature Priority
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free